Rear door heat exchanger

ABSTRACT

A rear door heat exchanger adapted to be mounted on the rear of a rack or other arrangement of heat-generating electronic equipment, and to cool air which passes therethrough when the rear door heat exchanger is in use. It comprises an upstream header and a downstream header with a multiplicity of substantially parallel microchannels extending between and in fluid communication with both the upstream header and the downstream header. Thus both headers are common to the microchannels of the said multiplicity of microchannels.

Data centers are traditionally cooled by perimeter cooling, in which airto liquid heat exchangers are situated around the perimeter of the roomand air is pumped from the interior of the data center to the heatexchangers, underneath the floor of the data center, and from thereupwards through air vents in the flooring into aisles between rows ofblade racks. Those aisles are therefore cool aisles. The cool air inthese aisles passes by convection between the blades and out through tothe other side of the row of racks, into a warm aisle. The warm air inthe warm aisles passes by convection to the air above the racks, alongthe ceiling and then downwards once again to the heat exchangers of theperimeter cooling. This cycle is continuous to keep the temperature ofthe center at an acceptably low level for efficient operation of theblades.

With increasing operational capacity of the blades, an increasing amountof cooling of the air in the data center becomes desirable or evennecessary. Simply increasing the cooling capacity of the perimetercooling is not necessarily an option because of limitation in the amountof cooling that can be effected in this way. This problem has beensolved by attaching respective air to fluid heat exchangers at the rearof the racks, where the air flow exits from the racks. Thus “rear” inthis sense refers to that side of the racks (or other heat generatingelectronic apparatus) from which cooling air exits. Such heat exchangersare referred to as rear door heat exchangers. The temperature of thecoolant supplied to existing rear door heat exchangers is usually aboutwhat would be considered normal room temperature or only slightly lower,typically in the region 18° C. to 22° C. This is still effective becausethe air temperature where it exits the blades is higher, perhaps in theregion of from 35° C. to 45° C.

Existing rear door heat exchangers comprise adjacent generallyvertically arranged upstream and downstream headers on one side of theexchanger with horizontal piping extending away from the upstream headerturning through 180° at the other side of the heat exchanger and thenextending horizontally to the downstream header. Such a constructioninvolves the use of piping of a relatively wide diameter and heavy metalcomponents which make the rear door heat exchanger cumbersome, expensiveto manufacture, and difficult to manoeuvre.

The present invention seeks to obviate one or more of these drawbacks,although it will be appreciated that the invention is effective for thecooling of air which has passed by any heat generating electronicequipment whether or not that equipment may fairly be referred to as ablade rack or blade racks.

Accordingly, embodiments of the present invention are directed to a reardoor heat exchanger adapted to be mounted on the rear of a rack or otherarrangement of heat-generating electronic equipment, and to cool airwhich passes therethrough when the rear door heat exchanger is in use,comprising an upstream header and a downstream header with amultiplicity of substantially parallel microchannels extending betweenand in fluid communication with both the upstream header and thedownstream header so that both headers are common to the microchannelsof the said multiplicity of microchannels.

This facilitates the construction of a light-weight rear door heatexchanger, more especially because the use of microchannels provides ahigh ratio of heat exchanger surface to cross-sectional area of coolantpassageway, and facilitates venting and draining of the heat exchanger.

Preferably the microchannels are upright when the rear door heatexchanger is mounted ready for use.

Insofar as the microchannels extend in a direction which has at least acomponent in the vertical direction, venting and draining of the heatexchanger is further facilitated.

The upstream header may be an upper header and the downstream header maybe a lower header.

Each microchannel may extend from the position where it is open to theupstream header to the position where it opens into the downstreamheader in a single pass without meandering.

This facilitates a high heat absorption capacity and operation of theexchanger with a relatively low pressure drop across the exchanger, andalso further facilitates venting and draining of the heat exchanger.

For the purposes of the present context, a microchannel will be deemedto be constituted by any passageway having an internal cross-sectionaldiameter or width of less than 3.5 mm. Preferably, the internalcross-sectional diameter or width of the microchannels is in the rangefrom 0.5 mm to substantially 3.0 mm. More preferably, the internalcross-sectional diameter of width of the microchannels is substantially1.1 mm or substantially 0.8 mm.

The interior of some or all of the microchannels may be rifled to givebetter heat transfer between the coolant and the microchannels.

One convenient construction for such a rear door heat exchanger isprovided by having the channels provided by tubes.

The rear door heat exchanger may be rendered more efficient by means ofstrips of material extending transversely of and in thermal contact withthe microchannels.

A good efficiency of the exchanger can be obtained if it comprises ametal or metal alloy. For example, the rear door heat exchanger maycomprise aluminium. Advantageously, for the improvement of venting anddraining of the channels, the upper header is the upstream header,although depending on site arrangement and performance requirements, theupstream header may be the lower header.

An example of a rear door heat exchanger embodying the present inventionwill now be described in greater detail with reference to theaccompanying drawings, in which:

FIG. 1 shows a perspective view from one side and from above of a datacentre incorporating rear door heat exchangers, each of which embodiesthe present invention;

FIG. 2 shows an underneath plan view of parts of the apparatus shown inFIG. 1;

FIG. 3 shows a perspective view from the rear, from one side and aboveof a part of the apparatus shown in FIGS. 1 and 2, with parts thereofdrawn transparent to reveal other parts;

FIG. 4 shows a front elevational view of a part of the apparatus shownin FIG. 3 with parts thereof removed for clarity;

FIG. 5 shows a side elevational view of the part of the apparatus shownin FIG. 4, with a side thereof being removed to reveal further parts;

FIGS. 6 a to 6 c show cross-sectional views of three differentembodiments of a part of apparatus shown in FIGS. 4 and 5; and

FIG. 7 shows an elevational front view of a part of the apparatus shownin FIGS. 4 and 5, on a larger scale;

FIG. 1 shows a data centre 100 provided with a chiller unit 110connected to supply cooling water to perimeter cooling 120. The datacentre 100 is provided with rows of blade racks 140, the blade racks 140being provided with respective rear door heat exchangers 142. Chilledwater from the chiller 110 is pumped through feed piping 143 to theperimeter cooling 120 and warm water returns from the perimeter cooling120 to the chiller 110 through further piping 144.

The perimeter cooling 120, and the blade racks 140 with their rear doorheat exchangers 142 rest on a raised floor 145. The blade racks 140 arearranged in rows 146. Air vents 148 are provided in the raised floor 145in one or more aisles 150 between rows 146, with adjacent aisles 152being without vents, so that aisles with vents alternate with thosewithout. When the data center 100 is in use, warm air in a warm aisle152 rises upwardly and draws with it through the racks 140 cool air fromthe adjacent cool aisles 150. This creates a continual draft of cool airthrough the racks 140. The warm air rises towards the ceiling of thedata center and outwardly towards the perimeter cooling 120 where it iscooled and therefore falls downwardly to exit the perimeter cooling 120underneath the raised flooring 145. This convection current continueswith the cool air rising upwardly through the vents 148 to continue theair cooling cycle.

The rear door heat exchangers 142 provide additional cooling of the airflowing through the data center 100.

A coolant distribution unit 200 distributes coolant to the rear doorheat exchangers 142. The manner in which it does this is more readilyseen from FIG. 2. Thus, the coolant distribution unit 200 is connectedto a primary coolant circuit 210 thermally coupled to a heat exchanger212 of the coolant distribution unit 200, and a secondary coolantcircuit 214 also coupled to the heat exchanger 212 of the coolantdistribution unit 200 such that heat is transferred from the coolant inthe secondary circuit 214 to the coolant in the primary circuit 210 whenthe apparatus is in operation. To this end coolant in the primarycircuit 210 is pumped through the coolant distribution unit 200 as iscoolant in the secondary coolant circuit 214.

Each rear door heat exchanger 142 is connected to receive coolant fromthe upstream side 216 of the secondary coolant circuit 214 by way of anupstream connector passageway 218 and to return coolant to thedownstream side 220 of the secondary coolant circuit 214 by way ofdownstream connectors 222.

FIG. 2 also shows internal fans 224 of the blade racks 140 which urgeair through the racks towards the rear door heat exchangers 142.

FIG. 3 shows outer panelling of a combination of a blade rack 140 and arear door heat exchanger 142 mounted on the rear thereof. The latter ishinged to the rack 140 on the left-hand side thereof as viewed in FIG.3. The rear panel 226 of the door 142 is perforated by a multiplicity ofperforations 228 to enable air to pass through the rear door heatexchanger 142. Because the latter is hinged to the rack 140 it isopenable to provide access both to the rear door heat exchanger 142itself and to the rear of the rack 140.

Further features of each rear door heat exchanger 142 are evidence fromFIGS. 4 and 5. Thus, it has a hinge 400 on its right-hand side as viewedin FIG. 4 and, in front of its rear panel 226 when viewed as in FIG. 4,an upstream header 402 to which is connected a vertically arranged partof the upstream connector 218, a lower downstream header 414 connectedto a vertical part of the downstream connector 222 and a multiplicity ofhollow bars or elongate extrusions 406 each providing a multiplicity ofmicrochannels. They are substantially parallel to one another and arearranged vertically, having upper ends in fluid communication with theinterior of the upper upstream header 402 and extending downwardly fromthere to their lower ends, without bends or meandering, which lower endsare in fluid communication with the interior of the lower downstreamheader 404. For the sake of clarity, not all of the microchannelextrusions 406 are shown, but only those to the left and to theright-hand sides of the rear door heat exchanger 142, the blank spacebetween those illustrated being filled with such microchannel bars.

A bleeder valve 408 is provided in the top of the upper upstream header402 and drain valve 410 is provided in the bottom of the lowerdownstream header 414.

Cooling U-shaped fins 412, only a few lines of which are showndiagrammatically in FIG. 4, each extend transversely of and are inthermal contact with the multiplicity of microchannel extrusions 406 atthe base of the ‘U’ of the fins 412. Such fins 412 are present all theway from the tops of the microchannel extrusions 406 to the lower endsthereof.

FIG. 6 a shows a cross-section of each microchannel extrusion 406. Thuseach extrusion is an aluminium extrusion and is elongate incross-section, being about 20 mm long and about 2 mm wide, with amultiplicity of microchannels 440 of generally rectangular crosssection, the width of each of which is about 1.4 mm, the thickness ofthe walls 442 of the bar 406 being about 0.3 mm. The outer shape of eachend channel in section is rounded, to follow the rounded ends 444 of thebar cross-section.

Each extrusion 406 is oriented so that its straight sides are generallyparallel to the direction of flow of air through the heat exchanger 142.

FIG. 7 shows the fins 412 more clearly, this Figure showing a front viewof an upper part of each heat exchanger 142. Fins of adjacentmicrochannel extrusions 406 interdigitate.

The vertical parts of the connectors 218 and 222, the headers 402 and414, the microchannel extrusions 406 and the fins 412 are all made ofaluminium. It will be appreciated therefore that because of the lightweight aluminium used, the rear door heat exchanger 142 as a whole isrelatively light. It is furthermore cheaper to construct and easier toinstall. Furthermore, the use of microchannels increases the outersurface area to internal volume ratio of the coolant passageways of therear door heat exchanger 142. Furthermore, the use of verticallyextending microchannels facilitates easy bleeding of air or other gasesfrom the rear door heat exchanger by way of the valve 408 and easydrainage of liquid coolant from the rear door heat exchanger 142 via thevalve 410. It will be appreciated that both the upper upstream header402 and the lower downstream header 404 are common to all themicrochannels 440.

When the apparatus is in use with air being circulated through the datacenter as described with reference to FIG. 1, and coolant being pumpedthrough the primary circuit 210 and the secondary circuit 214, coolantfrom the upstream side of the secondary circuit 214 passes into thevertical part of the upstream connector 218 of each rear door heatexchanger 142 to its upstream header 142, from whence it descendsthrough the microchannels of the microchannel bars 406 into the lowerdownstream header 404 and out through the vertical section of thedownstream connector 222 into the downstream side 220 of the secondarycircuit 214. Such passage of coolant through the rear door heatexchanger cools the air passing through the associated blade rack 140 asit passes through the rear door heat exchanger 142 and out through theperforated panel 326 into the warm aisle 152.

The coolant which may be used in each rear door heat exchanger 142 maycomprise water, or R134a refrigerant (1,1,1,2-tetrafluoroethane). Thelatter may be present in biphase condition (both in liquid and gaseousphase) in the microchannels of the microchannel extrusions 406.

Numerous variations and modifications to the illustrated apparatus mayoccur to the reader without taking the resulting construction outsidethe scope of the present invention. For example, each of themicrochannel extrusions may be provided with respective meanderingstrips instead of fins 412. Whilst the illustrated configuration callsfor a relatively small pressure differential between upper header 402and the lower header 404, the connections of the connectors 218 and 222can be reversed, so that the former is connected to the downstream side220 of the secondary circuit 214 and the connector 222 is connected tothe upstream side 216 of the secondary circuit 214, so that coolantflows upwardly through the microchannels of the microchannel bars 406instead of downwardly therethrough.

A preferred modified cross-section for the microchannel extrusion 406 isshown in FIG. 6 b and is 16 mm long, 1.8 mm wide, with eightsquare-sectional microchannels each of 1.12 mm width, with slightlyrounded corners, and two end microchannel sections being rounded ontheir outermost sides, the thickness of the walls of the bar being 0.34mm.

Another preferred modified cross-section for the microchannel extrusion406 is shown in FIG. 6 c and is 25.4 mm long, and 1.3 mm wide. It alsohas ten microchannels, the middle eight of which are rectangular insection, with slightly rounded corners, and are 1.88 mm long and 0.76 mmwide. The two end microchannels are also rounded at their outermostends. Thus the wall thickness of the bar along the longer sides of therectangle is 0.27 mm, and the wall thickness of the bar between adjacentmicrochannels is 0.6 mm.

The rear door heat exchanger 142 could clearly be reconfigured to behinged on the opposite side to that illustrated in the drawings.

Typically the temperature of the coolant in the upstream side 216 of thesecondary coolant circuit 214 when the apparatus is in use will besubstantially in the range from 10° C. to 25° C., preferably 15° C. to20° C., more preferably 18° C. The temperature of the coolant in thedownstream side 220 of the secondary coolant circuit 214 when theapparatus is in use will be substantially in the range from 20° C. to35° C., preferably 25° C. to 30° C., more preferably 28° C.

The cooling duty for bars as shown in FIG. 6 b in the apparatus of FIGS.4 and 5 is substantially in the range from 10 to 30 litres per minute(l/m), preferably 15 to 25 l/m, more preferably 20 l/m. That forextrusions as shown in FIG. 6 c is substantially in the range from 30 to50 litres per minute (l/m), preferably 35 to 45 l/m, more preferably 40l/m.

1. A rear door heat exchanger adapted to be mounted on a rear of a rackor other arrangement of heat-generating electronic equipment, and tocool air which passes therethrough when the rear door heat exchanger isin use, the exchanger comprising: an upstream header; a downstreamheader; and a multiplicity of substantially parallel microchannelsextending between and in fluid communication with both of the upstreamheader and the downstream header so such that both of the upstream anddownstream headers are common to the microchannels of the multiplicityof microchannels.
 2. A rear door heat exchanger according to claim 1, inwhich the microchannels extend in a direction which has at least acomponent in the vertical direction when the rear door heat exchanger ismounted ready for use.
 3. A rear door heat exchanger according to claim2, in which the microchannels are upright when the rear door heatexchanger is mounted ready for use.
 4. A rear door heat exchangeraccording claim 1, wherein the upstream header is an upper header andthe downstream header is a lower header.
 5. A rear door heat exchangeraccording to claim 1, wherein each microchannel extends from theposition where it is open to the upstream header to the position whereit opens into the downstream header in a single pass without meandering.6. A rear door heat exchanger according to claim 1, wherein eachmicrochannel has an internal cross-sectional diameter or width of lessthan 3.5 mm.
 7. A rear door heat exchanger according to claim 6, whereinthe internal cross-sectional diameter or width of each microchannel isin the range from substantially 0.5 mm to substantially 3.0 mm.
 8. Arear door heat exchanger according to claim 7, wherein the internalcross-sectional diameter or width of each microchannel is substantially1.1 mm.
 9. A rear door heat exchanger according to claim 7, wherein theinternal cross-sectional diameter or width of each microchannel issubstantially 0.8 mm.
 10. A rear door heat exchanger according to claim1, wherein the interior of at least one of the microchannels is rifledto give better heat transfer between the coolant and the microchannels.11. A rear door heat exchanger according to claim 1, wherein themicrochannels are provided by tubes.
 12. A rear door heat exchangeraccording to claim 1, further comprising strips of material extendingtransversely of and in thermal contact with the microchannels. 13.(canceled)
 14. (canceled)